The present invention relates to electrochemical cells, more particularly to thermal characteristics, such as heat dissipation, of electrochemical cells.
Secondary lithium-ion (Li-ion) battery cells possess a superior ability to source energy at high rates for extended periods of time, as compared with other electrochemical devices. An important challenge associated with Li-ion cells is thermal management. Cell performance and cell lifetime are both closely associated with cell temperature. Generally speaking, cell operation at cold temperatures results in reduced performance, and cell operation at high temperatures results in reduced lifetime. In addition, cell operation at high temperatures poses a risk of cell failure that is potentially very dangerous to personnel near the device. In order to ensure safe and reliable operation, a cell should be maintained at reasonable temperatures (e.g., at room temperature), and the temperature gradient within the cell itself should be kept to a minimum.
Li-ion cells are typically manufactured in either a prismatic or cylindrical shape. Cylindrical cells are commonly available on the commercial market ranging from small format cells (e.g., for laptops and power tools) to large format cells (e.g., for military use and electric vehicles). A major drawback of conventional cylindrical cell architecture is the difficulty for heat removal from the very center of the cell, due to the spiral windings internal to the cell. Conventional prismatic cells also tend to be deficient in shedding heat across (e.g., normal to) the adjacent layers, even those cells that are rather flat, e.g., similar to the shape of a notepad.
Conventional electrochemical cells constructed with layered electrode swirls (found in cylindrical cells) or stacks (in prismatic cells) tend to be characterized by good or sufficient thermal conductivity in the “in-plane” direction (i.e., in the geometric planes described by the electrode layers), but by poor or insufficient thermal conductivity in the “cross-cutting” or “out-of-plane” direction (i.e., across or perpendicular to the geometric planes described by the electrode layers). Cylindrical cells typically use layered electrode swirls (circular “jelly-rolls”). Prismatic cells typically use layered electrode stacks, but some prismatic cells use electrode swirls (flattened “jelly-rolls”) that are similar to those used by cylindrical cells. The prior art has focused upon improvement of heat transfer characteristics along the axial-longitudinal direction of the cell.
Of particular note are cylindrically wound cells that have been disclosed in the literature as having a central axial component that is solid or hollow and that extends partially or completely along the length of the cell. Such approaches to improving heat conduction characteristics of a cell seek to remove heat at the axial core of the cell using an axially-extended heat conductor. For instance, heat can be conducted by a device extending longitudinally-axially through a hollow core region of a cylindrical cell, or by a coolant medium that is passed through a pipe extending longitudinally-axially through a hollow core region of a cylindrical cell. While configurations of this nature may improve the ability of a cell (such as a cylindrical cell) to shed heat from the centermost regions, thermal conduction in the “out-of-plane” direction is usually the limiting factor.
The term “jelly-roll” is conventionally understood in battery cell arts to refer to the spiral-wound design characterizing most cylindrical secondary (rechargeable) batteries, such as lithium-ion (Li-ion) batteries, nickel-cadmium (NiCd) batteries, and nickel-metal hydride (NiMH) batteries. Some prismatic secondary batteries, as well, are characterized by a spiral-wound design of this kind. According to typical design of a cylindrical jelly-roll battery, a single electrode sandwich is rolled up and inserted into a hollow cylindrical casing, the cell is sealed, and metal contacts are attached. The sandwich has an anode material layer, a separator layer, and a cathode material layer; according to some conventional embodiments, the sandwich also has an insulating layer. In cross-section, the cylindrical battery resembles a jelly-roll cake. In a prismatic jelly-roll battery, the rolled-up electrode sandwich is flattened prior to insertion into a hollow prismatic casing. A jelly-roll design is usually used for secondary batteries, as distinguished from primary (non-rechargeable) batteries.
Pertinent references include the following patent documents, each of which is hereby incorporated herein by reference: Fuhr et al. U.S. Pat. No. 8,263,246 B2 (“Current Collector for an Electrochemical Cell”); Kim et al. U.S. Pat. No. 7,442,465 B2 (“Jelly-Roll Type Electrode Assembly, Lithium Secondary Battery Having the Same, and Method for Manufacturing the Same”); Hoffman et al. U.S. Pat. No. 6,117,584 (“Thermal Conductor for High-Energy Electrochemical Cells”); Romero et al. U.S. Pat. No. 6,020,084 (“Electrochemical Cell Design with a Hollow Core”); Oweis et al. U.S. Pat. No. 5,972,532; Teramoto et al. U.S. Pat. No. 5,501,916 (“Battery Having a Through-Hole and Heat Dissipating Means”); Sugalski U.S. Pat. No. 4,322,484 (“Spiral Wound Electrochemical Cell Having High Capacity”); Ramamurthi et al. U.S. Patent Application Publication No. 2012/0301768 A1 (“Battery Cell Design and Method of Cooling Battery Cells”); Yoon et al. International Patent Application (PCT) No. WO 2013/152149 A1 (“The Lithium Ion Prismatic Cell Comprising Multiple Jelly-rolls with Additional Material between Jelly-rolls”).